Selective reduction of NOx with hydrocarbons over Ir catalyst supported onMFI-type metallosilicates

Iridium catalysts supported on MFI-type metallosilicates were prepared and their catalytic activity far the selective reduction of NOx with hydrocarbo ns under oxygen rich condition was investigated. The as-prepared catalyst h ardly reduces NOx to N-2 though it showed very high activity for the hydroc arbon conversion with oxygen. After subjecting the activation treatment in 10%H2O-N-2 at 700 degrees C, on the other hand, the activated catalyst show ed very high NOx reduction activity. The activated catalyst selectively and efficiently reduced NOx to N-2 with olefinic and aromatic hydrocarbons at 300-500 degrees C in the stoichiometric to lean conditions. The characterization by XRD and EXAFS revealed that their species existed i n the form of oxide (IrO2) and metal in the as-prepared and activated catal ysts, respectively. In addition, H-2-TPR measurement showed that: the activ ated catalyst had active oxygen species on the Ir metal surface which was m ore reactive (reducible) than oxygen species on IrO2 and bulky Ir metal. It was inferred that the high NOx reduction activity of the activated catalys t resulted from the presence of the active oxygen species which might react with hydrocarbons to form reactive oxygenated intermediates.